The field of the disclosure is related to systems and methods for controlling particles. More particularly, the disclosure relates to systems and methods for trapping particles using projected light.
The ability to confine and manipulate particles using optical techniques has paved the way for a number of scientific advancements. For instance, defect-free artificial crystals have been created using trapped particles, and used to investigate various fundamental principles governing interactions and material properties. Neutral atoms have been particularly attractive because of their well-defined quantum structure and charge neutrality. Charge neutrality isolates atoms from charge-related perturbations, and helps to retain quantum information for longer times. In addition, neutral atoms can be controlled individually, and scaled to large systems.
An atom becomes trapped by the coherent interactions between the electromagnetic fields of applied light, and oscillating electric dipole moment induced in the atom. Specifically, the electromagnetic fields induce internal atomic energy shifts that generate effective potentials from which confinement forces arise. To trap the atom, the frequencies of the light are typically shifted, or detuned, with respect to the atomic resonance frequencies. In particular, when the frequency of the light is below an atomic transition frequency, or “red detuned,” the induced atomic dipole moment is in-phase, and the atom becomes attracted to the intensity maxima of the light. The attraction strength is dependent upon the magnitude of detuning. By contrast, when the frequency is “blue detuned,” the induced moment is out of phase, and the atom is repelled from the maxima. In addition, the strength of attraction/repulsion can be modified by controlling the intensity or power of the applied light.
Optical techniques have also been widely used for trapping arrays of atoms for quantum computing and atomic clock applications. Arrays have been prepared in 1-, 2-, or 3-dimensional configurations or optical lattices. Bright, red detuned, arrays localize atoms at the local maxima, while dark, blue detuned, arrays localize the atoms at local minima. In general, dark arrays require more complicated optical systems, but offer the important advantage that by localizing atoms where the intensity is low, there is less perturbation. This is significant for extending the coherence time of atomic qubits and for minimizing disturbance to atoms in optical clocks.
Optical lattices are commonly formed by the interference of light from different sources. For example, a 1D lattice can be created using a standing wave generated by superposing two counter-propagating laser beams. Higher dimensional optical lattices require additional optical sources. For example, a 3D simple-cubic lattice structure can be produced by overlapping three orthogonal standing waves formed using 3 pairs of counter-propagating optical sources. However, atomic positions in a lattice generated by the interference of counter-propagating beams are very sensitive to optical path-length. Slight drifts can cause differential phase shifts between beams, and significantly affect the atomic positions. Although phase shifts can be, in principle, compensated by using active stabilization, such techniques are commonly applied to single atoms. This is because of the increased system complexity required for performing active stabilization on multiple atoms.
The position of the interference fringes is sensitive to the relative phase of the interfering light beams, and is thus sensitive to optical path lengths. Such sensitivity may be removed by projecting intensity patterns that do not require interferometric stability. However, projected light forms more than one plane of optical traps due to the Talbot effect, which arises from the periodic nature of phase coherent light repeating in free space. This can lead to unwanted atom trapping in multiple spatial planes. In attempting to suppress this effect, some prior techniques have utilized different frequencies of light for each optical trap, or spatial light modulators to impart random phases to each trap. However, such approaches require a number of components (e.g. acousto-optic deflectors, spatial light modulators, diffractive, polarization sensitive optical components, and so on) that add significant system complexity and cost.
Given the above, there is a need for systems and methods for particle confinement that are simple to implement and avoid undesired effects, such as position drifts due to optical phase fluctuations, crosstalk, and the Talbot effect.